1. Field of the Invention
This invention relates to a process and an apparatus for forming aerosols of vaporizable solid-state pesticidal chemicals, and more specifically, to a process and an apparatus suited for forming aerosols of fungicides or insecticides.
The process of this invention may be applied to a wide variety of solid-state pesticidal chemicals so long as they can be formed into aerosols.
2. Description of the Prior Art
Recently, the application of pesticides in aerosol formulations has received increasing interest in the art and has been used with a wide variety of pesticides as well as fumigants as an effective means for controlling fungi, bacteria, and insects, not only in enclosed rooms such as warehouses and greenhouses, but also in open fields.
In general, processes for the application of pesticides in the form of aerosols, fogs, or atomized particles can be classified into the following types:
A. spraying the solution of pesticides (e.g., fungicides, insecticides or both) dissolved in a liquefied gas enclosed in a vessel, by utilizing the vapor pressure of the liquefied gas; PA1 B. atomizing the solution of pesticides by means of mechanical atomization; PA1 C. vaporization of pesticides in mixture with combustible materials by the heat of combustion; and PA1 D. vaporization of pesticides by indirect heating.
None of these known processes are completely satisfactory.
For example, process (a) has drawbacks of (i) requiring a liquefied gas in which the pesticide is dissolved, (ii) compression in a confined container, and (iii) the high cost of the liquefied gas and difficulty of handling, etc. Process (b), though being used practically in rather wide fields, still finds limited utility since it requires high pressures to atomize the pesticides finely, and a particular solvent which must (i) be inexpensive and (ii) easily handled. Process (c) has been applied as a formulation comprising a suitable mixture of pesticide with combustible materials, such as sugars, zinc dust, aluminum dust, wood powder, celluloid and similar organic materials, and optionally with an added oxygen-carrier such as salts or esters of nitric acid, perchlorate salts, chlorate salts, bichromates, peroxides, etc. Process (d) is applied by heating the pesticide directly on a heated plate or heated tube through which a liquid pesticide is passed.
The last two processes are advantageous from the viewpoint of manpower savings, but suffer from the following drawbacks:
The effect of the pesticide is greatly reduced during combustion or heating in an oxidative atmosphere, such as air, a heating mixture or a hot combustion gas, because of the oxidative decomposition of the pesticide. Moreover, excessive heating of the pesticide is inevitable at this time, and results in the acceleration of the thermal decomposition of the pesticide. The by-products formed as decomposition products during the combustion or heating of the pesticides quite often have hazardous influences on plants.
For these reasons, there has long been a demand in the art for an improved process for forming aerosols of pesticidal chemicals.